I recently bought a Yamaha ef2000i genset to replace our old homelight hg600. Love the yamy so far. I was getting the hg600 ready to list for sale and thought I'd check all the outputs and document them for the prospective buyer. All seamed well with it. I then thought for the fun of it to check the yamy.... It read 19.63vdc in econo mode and 27.16vdc on high!!! I read and re read the manual. I hooked it to my 2 T105's and checked it again. After about 1.5 min the voltage was at 15.5vdc and climbing steadily. I pulled the plug at that point out of fear. The batteries were also charged using a quality charger and checked with a hydrometer. I have never used the battery charging port on a geny but want it to work if I need it. Am I missing something? Or is the genset messed up?

I agree, don't use the 12 v outlet for charging, just run the gen set and plug a battery charger into the gen set 120 outlet or plug the RV into the gen set and let the onboard Converter charge the batteries.

If the charging circuit is the same as Honda's, and there's a reasonable chance that it is, the output is unfiltered and unregulated DC. Without a good load, different meters give different readings. Before the current wave of power converters and smart chargers, most plug-in chargers had this same type of output. For comparison, my eu2000i, with eco mode off and a 2.5 amp load reads 27 volts peak on an oscilloscope, 27 volts on an analog multimeter, and 14.2 volts on an RMS meter. It's the RMS reading that counts. With no load, the multimeter reads 30 volts, pretty similar to the Yammy. I'm no battery expert but think if the battery isn't boiling like crazy you're not charging it too heavily. I agree that it's best to use a good charger, but when you're stuck with a dead battery and don't have a charger available, that charging output is pretty darn valuable.

Don't use the 12V output for battery charging. It doesn't put out that many amps anyways, you'd have to charge it for a week. Just plug your trailer cord into the generator. The trailers converter will do a MUCH better job (unless you have 70 feet of wiring between the converter and the batteries).

Thank you for your very informative post Wayne. I prefer to charge with a good charger or converter. It's nice to know that in a pinch for whatever reason I can charge with the genset battery charge plug as a backup if needed. I won't stress now that my genset is wonky. Thanks again!

mtnbiker1096 wrote:Thank you for your very informative post Wayne. I prefer to charge with a good charger or converter. It's nice to know that in a pinch for whatever reason I can charge with the genset battery charge plug as a backup if needed. I won't stress now that my genset is wonky. Thanks again!

2x on Wayne's test results showing it safe to use the DC output if required.

Last year somebody posted about using the Honda DC for equalizing so I tried it with the Honda EU3000i. I never thought to take the unloaded DC voltage.

Battery voltage on "full" batteries rose to the 16s with Eco and the 17s on full power. But once to those voltages, the voltage stayed there not rising any more. It does not take long to get the batteries bubbling, and it worked as an equalize charge of short duration.

So it seems safe to use to charge low batteries. An hydrometer can tell you when they are close to full and then you can stop.